What is full frame? It means that the sensor inside the D600 is the same size as a frame of 35mm film.
This larger-size sensor is capable of capturing images with blurrier
backgrounds and higher image quality, especially in low-light
situations.

Previously full-frame cameras were designed specifically for
professional working photographers: they were big, heavy, feature-rich
and very expensive.

The Nikon D600 aims to bring full frame down a notch, from the "professional" level to the "enthusiast" level — people who really like taking pictures but aren't charging thousands of dollars to shoot weddings.

Does it succeed? Somewhat: the Nikon D600 has a body size
and shape that is closer in scale to the immensely popular Nikon D7000.

However, the price - still above $2,000 USD for the body only is still well above what many people can afford.

Simply put: you have to really want a full-frame camera and have the skills to use it to justify dropping this much cash on a digital camera.